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- Earthquakes occur when the plates that make up the Earth's crust move around. These plates, called tectonic plates, can push against each other. Earthquakes are most common along fault lines, which are fractures that allow the plates to move.
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Apr 5, 2024 · U.S. What causes earthquakes? The science behind why seismic events like today's New Jersey shakeup happen. By Kerry Breen. Updated on: April 5, 2024 / 6:40 PM EDT / CBS News. A strong earthquake...
- kerry.breen@paramount.com
- 8 min
- News Editor
- Kerry Breen
- Overview
- Where do most earthquakes occur?
- Fault types
- Earthquake magnitude ratings
- Earthquake damage
Thousands of temblors occur every day. Here’s what you need to know about where they usually take place and how they're measured.
Thousands of earthquakes occur every day. Most are too minor to feel but strong earthquakes can cause massive destruction—like this bridge that collapsed in Taiwan after an magnitude 6.8 earthquake in September 2022 caused severe damage across the country.
Earthquakes, also called temblors, can be so tremendously destructive that it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors. Most are so small that humans can't feel them.
But every so often, a big quake will strike—most recently a 7.8-magnitude earthquake that struck southern Turkey and Syria on February 6, 2023, which scientists tell Reuters is likely to be one of the deadliest of this decade. Here's what you need to know about where earthquakes typically occur, how earthquakes are measured, and the damage that the strongest earthquakes can cause.
Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "ring of fire" because of the preponderance of volcanic activity there, as well. Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make up Earth's upper layer—collide or slide against each other.
These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from fault zones when plates are stretched or squeezed.
There are several different types of faults, including a normal dip slip fault, reverse fault, and strike-slip fault. Here's what they mean.
Strike-Slip
When portions of the Earth's crust moves sideways, the result is a horizontal motion along a "strike-slip" fault.
The most famous example is California's San Andreas Fault, which stretches some 600 miles (1,000 kilometers) from southern California to north of San Francisco. The sideways motion of the fault's branches is caused by the Pacific Ocean's crustal plate moving to the northwest under North America's continental crust.
Dip-Slip
Up-and-down motions in earthquakes occur over so-called "dip-slip" faults, where the ground above the fault zone either drops (a normal fault) or is pushed up (a reverse fault). A normal fault occurs where the deeper part of the crust is pulling away from an overlying part. A reverse is, well, just the reverse.
Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves. A quake measuring 3 to 4.9 is considered minor or light; 5 to 6.9 is moderate to strong; 7 to 7.9 is major; and 8 or more is great.
Earthquakes are always followed by aftershocks, which are smaller quakes that strike after the main quake and can continue for weeks—or even up to years in some cases. According to the USGS, some earthquakes also have foreshocks, or smaller quakes that precede a larger earthquake.
4:46
Earthquakes 101
Earthquakes can leave behind incredible devastation, while also creating some of the planet's most magnificent formations. Learn about the geophysics behind earthquakes, how they are measured, and where the most powerful earthquake ever witnessed occurred.
The strongest earthquake ever recorded was a magnitude 9.5 quake that struck southern Chile in 1960. The Valdivia earthquake—named for the city that suffered the most damage—killed about 1,655 people and left another two million homeless. It also triggered a tsunami that spread across the Pacific and flooded coastlines in Japan, Hawaii, and New Zealand.
On average, a magnitude 8 quake strikes somewhere every year, and some 10,000 people die in earthquakes annually. Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can complicate rescue efforts and cause further death and destruction.
Loss of life can be avoided through emergency planning, education, and the construction of buildings that sway rather than break under the stress of an earthquake.
— Amy McKeever and Dan Vergano contributed to this story.
Editor's note: This story was originally published on July 4, 2019. It has been updated.
- 5 min
Apr 23, 2024 · Earthquake, any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks. Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another. Learn more about the causes and effects of earthquakes in this article.
- Why is an earthquake dangerous?Over the centuries, earthquakes have been responsible for millions of deaths and an incalculable amount of damage to property. Depending on their i...
- What are earthquake waves?Earthquake waves, more commonly known as seismic waves, are vibrations generated by an earthquake and propagated within Earth or along its surface....
- How is earthquake magnitude measured?Magnitude is a measure of the amplitude (height) of the seismic waves an earthquake’s source produces as recorded by seismographs. Seismologist Cha...
- Where do earthquakes occur?Earthquakes can occur anywhere, but they occur mainly along fault lines (planar or curved fractures in the rocks of Earth’s crust), where compressi...
Sep 14, 2023 · In February 2023, a large area of Turkey and Syria was devastated by two major earthquakes that hit in close succession. As a geologist, I study the forces that cause earthquakes. Here’s why ...
- Jaime Toro
Jun 12, 2021 · What is an earthquake? Earthquakes are the result of a fault line moving and releasing energy, or as Julian Lozos, assistant professor of geophysics at Cal State Northridge,...
Also called a temblor, an earthquake is caused by the movement of parts of the Earth’s crust, its outermost layer. They happen millions of times a year, but most are so...
Sep 14, 2023 · In February 2023, a large area of Turkey and Syria was devastated by two major earthquakes that hit in close succession. As a geologist, I study the forces that cause earthquakes. Here's why some...
